Preparation time: 15 minutes
Cooking time: 10 minutes
Resting time: 1 hour

Storing: It will keep for several months in a tightly-closed container at a moderate temperature. Avoid heat, which will turn the almond and hazelnuts oils rancid and make the paste unusable.

This paste is a staple of pastry and confectionery making. It can also, in moments of pure gourmandise, be used as a spread.

1. In a non-stick pan, toast the hazelnuts and almonds to bring out all their flavor. You could also place them into a 200° C (400° F) oven for 15 minutes.
2. Place the sugar and water into another non-stick pan; heat gently over medium heat without stirring.
3. When the sugar begins to dissolve, add the almonds and hazelnuts. Mix well with a spatula and cook until the sugar is completely dissolved and the mixture forms a light caramel (160° C / 320° F). This process should be carried out over medium heat, otherwise the caramel will become too dark. The darker it is, the stronger its flavor.  
4. Pour the mixture onto a lightly oiled marble slab or a baking sheet covered with parchment paper and let cool for 1 hour.
5. Break the mixture into pieces and grind it finely in a food processor. Continue processing until it forms an oily paste. It's best to divide the mixture into three parts and to grind them for 5 minutes at a time to avoid overworking your food processor.

Chocolate praline paste
Mix 55 g of dark chocolate into the paste during the last step. 

Professional version 
Place 50 ml water, 25 g glucose and 225 g sugar into the saucepan and mix over the heat until it comes to a boil. 
Cook the sugar to a light caramel (160° C / 320° F). Add 125 g each of almonds and hazelnuts to the caramel and combine with a spatula. Proceed as above.  

Variations
For a milder praline paste, you can pulverize the toasted almonds and hazelnuts in a food processor with an equal weight of icing sugar (250 g), with no water and with no caramelization (this is called "raw sugar" praline paste).

You can also vary the proportion of sugar with no problem (e.g., 60% sugar, 40% nuts), or vary the nuts, using all almonds or all hazelnuts, for instance, or even walnuts, pine nuts, peanuts, etc. The method remains the same.